Therapeutic and/or preventive agents for diseases due to retinal ischemia

ABSTRACT

An agent for treating and/or preventing for diseases (glaucoma, diabetic retinopathy, macular degeneration, retinal vascular obstruction, and the like) due to retinal ischemia, which comprises, as an effective ingredient, (2R)-N-(1-benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamide represented by the following formula (I):  
                 
 
     or a nontoxic salt thereof.

TECHNICAL FIELD

[0001] The present invention relates to an agent for treating and/orpreventing diseases due to retinal ischemia.

[0002] More specifically, the present invention relates to an agent fortreating and/or preventing diseases due to retinal ischemia, whichcomprises, as an active ingredient,(2R)-N-(1-benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamide represented by the following formula(I):

[0003] or a non-toxic salt thereof.

BACKGROUND ART

[0004] The retina is phylogenetically belongs to the diencephalon and isonly one central nervous system that can be directly observed from theoutside. The retina is a tissue extremely suited for the study ofneuronal network, because different from the brain and spinal cord whichparticipate in plural functions, the retina participates in only asingle function; visual perception, and its cells for providing visualinformation to the brain are limited to five types: visual cells,bipolar cells, ganglion cells, amacrine cells, and horizontal cells.Therefore, a number of neurophysiological studies have been made withthe retina as an object. Moreover, the retina occupies an importantposition in the ophthalmic diseases.

[0005] In the past, main ophthalmic diseases were external eyeinfections such as trachoma. In recent years, however, the proportion ofdiseases related to visual function has shown an increasing trend.Diseases which cause a deterioration in visual function can be roughlyclassified into functional diseases such as ametropia (myopia,hyperopia, astigmatism and the like) and accommodation abnormal(presbyopia and the like), and organic diseases such as cataract andglaucoma. Among these diseases, retinal diseases including glaucoma arethe most common cause of blindness in the world. In particular, glaucomais a typical disease which narrows the visual field due to neuronaldeath of the retina and its main cause has been considered to be amechanical injury which occur as a result of an increase in intraocularpressure due to impaired outflow of aqueous humor.

[0006] In addition to the mechanical damage as described above,glutamate-induced neurocytotoxicity due to retinal ischemia has recentlycome to be recognized as one of the important causes for retinaldisorders in glaucoma. Such a recognition has appeared, because clinicalfindings which cannot be explained by the theory of mechanical disorderdue to an increase in intraocular pressure have been reported, forexample, that it is difficult to completely inhibit the progress of avisual field loss due to retinal disorders even if the intraocularpressure is lowered to a normal range; or that as in the case of lowtension glaucoma, symptoms of glaucoma appear even when the intraocularpressure falls within the normal range or lower. There is accordingly ademand for the development of not only medical treatment for loweringintraocular pressure but also a medicament directly acting on theretina. However, studies on neuroprotective agents which act on theretina are very rare at present.

[0007] On the one hand, a model of retinal disorders due to transientretinal ischemia plays an important role among retinal disorder models.As a result of a study on the effect of the compound represented by theformula (I) using the model, it has exhibited curative effects forretinal disorders by inhibiting retinal neuronal death.

[0008] Accordingly, the compound represented by the formula (I) whichhas curative effects for retinal disorders is considered to be useful asa remedy and/or preventive for many ophthalmic diseases (glaucoma,diabetic retinopathy, macular degeneration, retinal vascularobstruction, etc.) in which involvement of neuronal death due to retinalischemia has been pointed out.

[0009](2R)-N-(1-Benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamiderepresented by the formula (I) is a compound described in Example 2 inthe specification of WO00/00470 as an amino acid derivative having an Ntype calcium channel blocking activity.

[0010] According to the description in the specification, the amino acidderivative having an N type calcium channel blocking activity iseffective as an agent for preventing and/or treating cerebralinfarction, transient cerebral ischemic attack, cerebrospinal disordersafter cardiac surgery, spinal blood vessel abnormalities, stress-relatedhypertension, neuropathy, epilepsy, asthma and pollakiuria, or ananalgesic. However, there is no description that the compoundrepresented by the formula (I) or a non-toxic salt thereof is effectivefor diseases due to retinal ischemia (glaucoma, diabetic retinopathy,macular degeneration, retinal vascular obstruction, etc.).

DISCLOSURE OF THE INVENTION

[0011] As a result of intensive investigation, the inventors of thepresent invention have found for the first time that(2R)-N-(1-benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamiderepresented by the formula (I) or a non-toxic salt thereof is effectivefor diseases due to retinal ischemia and thus completed the presentinvention.

[0012] Thus, the present invention relates to an agent for treatingand/or preventing diseases due to retinal ischemia, which comprises, asan effective ingredient, (2 R)-N-(1-benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamiderepresented by the following formula (I):

[0013] or a non-toxic salt thereof.

[0014] The compound represented by the formula (I) may be administeredas a salt. As the salt, non-toxic and water-soluble ones are preferred.

[0015] Examples of the non-toxic salts include alkali metal salts,alkaline earth metal salts, ammonium salts, amine salts and acidaddition salts.

[0016] Suitable salts include salts of alkali metals (potassium, sodium,etc.), salts of alkaline earth metals (calcium, magnesium, etc.),ammonium salts, and salts of pharmaceutically acceptable organic amines(tetramethylammonium, triethylamine, methylamine, dimethylamine,cyclopentylamine, benzylamine, phenethylamine, piperidine,monoethanolamine, diethanolamine, tris(hydroxymethyl)aminomethane,lysine, arginine, N-methyl-D-glucamine, etc.).

[0017] Suitable acid addition salts, for example, include salts ofinorganic acids such as hydrochlorides, hydrobromides, hydroiodides,sulfates, phosphates and nitrates and salts of organic acids such asacetates, lactates, tartrates, benzoates, citrates, methanesulfonates,ethanesulfonates, benzenesulfonates, toluenesulfonates, isethionates,glucuronates, and gluconates.

[0018] The compound represented by formula (I) and salts thereof may beconverted into the corresponding solvates. As the solvates, non-toxicand water-soluble ones are preferred.

[0019] Suitable solvates include solvate salts with a solvent such aswater or alcohol (e.g., ethanol, etc.).

[0020] [Preparation Process of an Effective Ingredient]

[0021](2R)-N-(1-Benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamiderepresented by the formula (I) or a non-toxic salt thereof can beprepared in accordance with the process as described in the process asdescribed in the specification of WO00/00470.

[0022] [Toxicity]

[0023] The compound represented by the formula (I) or a non-toxic saltthereof has markedly low toxicity so that use of it as a pharmaceuticalcan be considered as safe enough. For example, the minimum lethal doseof the compound represented by the formula (I) by single-dose oraladministration to rats was 2000 mg/kg or more.

INDUSTRIAL APPLICABILITY

[0024] [Application to Pharmaceuticals]

[0025] As the compound represented by the formula (I) or a non-toxicsalt thereof has curative effects on retinal disorders, it is consideredto be useful as an agent for treating and/or preventing a number ofophthalmic diseases (glaucoma, diabetic retinopathy, maculardegeneration, retinal vascular obstruction, etc.) in which involvementof neuronal death due to retinal ischemia has been pointed out.

[0026] When the compound represented by the formula (I) or a non-toxicsalt thereof according to the present invention is used for theabove-described purpose, it is usually administered systemically ortopically via an oral or parenteral route.

[0027] Although the dose differs, depending on age, weight, symptom,desired therapeutic effects, administration route, duration of treatmentand the like, the compound is usually administered orally at a singledose of 1 mg to 1000 mg per adult once or several times a day; isparenterally administered (preferably, by eye drops) at a single dose of1 mg to 100 mg per adult once or several times a day; or isintravenously administered continuously for 1 to 24 hours a day.

[0028] As described above, the dose varies, depending on variousconditions, so that the dose smaller than the above-described dose maybe sufficient amount and the dose exceeding the above-described rangemay be required.

[0029] Upon administration, the compound represented by the formula (I)or a non-toxic salt thereof is used as solid compositions, liquidcompositions or other compositions, each for oral administration, or aseye drops, eye ointments, injections, external preparations orsuppositories, each for parenteral administration.

[0030] The solid compositions for oral administration include tablets,pills, capsules, powders, granules and liquids.

[0031] The capsules include hard capsules and soft capsules.

[0032] Such solid compositions are prepared by mixing one or more activesubstances with at least one inert diluent such as lactose, mannitol,glucose, hydroxypropyl cellulose, microcrystalline cellulose, starch,polyvinyl pyrrolidone or magnesium aluminometasilicate. The compositionsmay contain, in accordance with the conventional process, additivesother than the inert diluent, for example, lubricant such as magnesiumstearate, disintegrant such as calcium cellulose glycolate, stabilizersuch as lactose and solubilizing agent such as glutamic acid or asparticacid. Tablets or pills may be coated with a film of a gastric soluble orenteric substance such as sucrose, gelatin, hydroxypropyl cellulose orhydroxypropyl methylcellulose phthalate, or with two or more layers, ifnecessary. Furthermore, capsules made of a substance which can beabsorbed in the body, for example, gelatin, is included.

[0033] Liquid compositions for oral administration includepharmaceutically acceptable emulsions, solutions, syrups and elixirs.Such liquid compositions contain one or more active substances and anordinarily employed inert diluent (for example, purified water orethanol) dissolving the substances therein. These compositions maycontain, in addition to the inert diluent, an adjuvant such as ahumectant or suspending agent, a sweetening agent, a flavoring agent, anaromatic agent and antiseptic.

[0034] The other compositions for oral administration include sprayswhich contain one or more active substances and are formulated in amanner known per se in the art. These compositions may contain, inaddition to an inert diluent, a stabilizer such as sodium bisulfite andan isotonic buffer such as sodium chloride, sodium citrate or citricacid. The preparation process of sprays is described in detail in, forexample, U.S. Pat. Nos. 2,868,691 and 3,095,355.

[0035] The dosage form of eye drops for parenteral administrationinclude ophthalmic solutions, ophthalmic suspensions, ophthalmicemulsions and ophthalmic solutions dissolved before use.

[0036] Such eye drops are prepared in a known method. For example, anophthalmic solution is prepared by selecting proper additives from anisotonizing agent (such as sodium chloride or concentrated glycerin), abuffering agent (such as sodium phosphate or sodium acetate), asurfactant (such as “Polysorbate 80” (trade name), polyoxyl 40 stearateor polyoxyethylene hydrogenated castor oil), a stabilizer (such assodium citrate or edetate sodium) and an antiseptic (such asbenzalkonium chloride or p-aminobenzonic acid), if necessary. They aresterilized or subjected to aseptic manipulation in the final step.

[0037] For the eye ointments, a known ointment base such as purifiedlanolin, vaseline, plastibase, liquid paraffin or polyethylene glycolmay be used.

[0038] Injections for parenteral administration include sterile aqueousand/or non-aqueous solutions, suspensions and emulsions. The aqueoussolutions or suspensions include, for example, distilled water forinjection and saline. The non-water soluble solutions or suspensionsinclude vegetable oils such as propylene glycol, polyethylene glycol andolive oil, alcohols such as ethanol and “Polysorbate 80” (trade mark).Sterile aqueous and non-aqueous solutions, suspensions and emulsions maybe used in combination. Such compositions may additionally containadjuvants such as antiseptic, humectant, emulsifier, dispersant,stabilizer (such as lactose) and solubilizing agent (such as glutamicacid and aspartic acid). They are sterilized by filtration through abacteria retaining filter, by the addition of a sterilizer, or byirradiation. They may be prepared in the form of a sterile solidcomposition such as a freezed-dried product, which may be dissolved insterile distilled water for injection or another sterile solvent beforeuse.

[0039] The other compositions for parenteral administration comprise oneor more active ingredient and include liquid preparations for externaluse; ointments, endermic liniments, suppositories for intrarectaladministration and pessaries for intravaginal administration which areformulated in a conventional method.

BEST MODE FOR CARRYING OUT THE INVENTION

[0040] The present invention will be described specifically by anexperimental example. However, that the present invention is not limitedthereto.

[0041] Effects of the compound represented by the formula (I) (whichwill hereinafter be called “compound of the present invention”) on a ratmodel with retinal disorders due to transient retinal ischemia;

[0042] [Testing Method]

[0043] The model with retinal disorders due to transient retinalischemia was prepared in accordance with the method described in Eur. J.Pharmaco., 350, 53-57 (1998).

[0044] After rats (SD male rats, 9-week-old (purchased from CharlesRiver Japan, Inc.)) were weighed, pentobarbital sodium (Pentbarbital Na)(50-75 mg/kg) was intraperitoneally administered to anesthetize them.They were fixed to a platform, and kept warm at around 37° C. Aperfusate for ophthalmic surgery (“BSS PLUS”; product of SantenPharmaceutical) was hung so that the height from the position of theeyes of the rats would be 170 cm±5 cm. This height permitted applicationof pressure of about 130 mmHg. To the perfusate bottle was connected anextension tube and an injection needle (27 gauge×¾ inch) was attached toanother end of the tube. After pupillary dilatation, the needle wasinserted into the anterior chamber of eye from the nose side while theeyelid was opened with forceps and an ischemic burden was applied for 45minutes (the left eye was treated, while the right eye was leftuntreated). The compound of the present invention was administered onehour before ischemia was caused. One week after completion of theischemia treatment, the animals were sacrificed with anesthesia andthen, the eyeballs were excised.

[0045] After the eyeballs were immobilized in a Davidson's fixative anda paraffin section was prepared at the cross-section passing through theoptic papilla, it was dyed with hematoxylin and eosin (H.E.).Photographs of all the cases were taken. The number of granule cells(GCL (ganglion cell layer), cell/mm) per 1 mm width of the optic papillawas counted by optical microscopic examination.

[0046] The constitution of the groups and the number of animals are asfollows: a compound of the present invention group and a control group,each group consisting of 5 animals, and 10 animals in total.

[0047] An aqueous 0.5% carboxymethyl cellulose (0.5% CMC) solution ofthe compound of the present invention was orally administered at a doseof 100 mg/5 mL/kg, while to the control group was orally administered a0.5% CMC aqueous solution at a dose of 5 mL/kg.

[0048] The results are shown in Table 1. TABLE 1 The number of granulecells (GCL) (cell/mm) Untreated 67.4 Control 40.0 Compound of thepresent invention 49.2

[0049] As is apparent from the above Table 1, the compound of thepresent invention exhibited a 34% inhibiting activity to the model ofretinal disorders due to transient retinal ischemia.

[0050] From the results of Table 1, it has been understood that thecompound represented by the formula (I) used in the present inventioninhibits death of granule cells in the rat model of retinal disordersdue to transient retinal ischemia. This suggests that the compoundrepresented by the formula (I) or a non-toxic salt thereof is effectivefor the treatment and/or prevention of diseases (glaucoma, diabeticretinopathy, macular degeneration, retinal vascular obstruction, etc.)due to retinal ischemia.

1. An agent for treating and/or preventing of a disease due to retinalischemia, which comprises, as an effective ingredient,(2R)-N-(1-benzylpiperidin-4-yl)-3-cyclohexylmethylthio-2-((4R)-3-t-butoxycarbonylthiazolidin-4-ylcarbonylamino)propanamiderepresented by the following formula (I):

or a nontoxic salt thereof.
 2. The agent according to claim 1, whereinthe disease due to retinal ischemia is glaucoma, diabetic retinopathy,macular degeneration, or retinal vascular obstruction.